Hemolysis (microbiology)

Encyclopedia : H : HE : HEM : Hemolysis (microbiology)

Examples of alpha (top), beta (middle), and gamma (bottom) hemolysis on sheep blood agar plates

Hemolysis is used in the empirical identification of microorganisms based on the ability of bacterial colonies grown on agar plates to break down red blood cells in the culture. When the organism has been grown on blood agar plates, it can be classified with regard to whether or not it has caused hemolysis in the red blood cells (RBCs) incorporated in the medium. This is of particular importance in the classification of streptococcal species.

While a blood agar plate may contain varying concentrations of RBCs and may use blood from a variety of animals, clinical results are most often reported on 5-10% sheep blood agar plates (SBAP).

Types of hemolysis

Alpha hemolysis (α-hemolysis) is present if there is a greenish darkening of the agar under the colonies. Streptococcus pneumoniae displays alpha hemolysis. This is sometimes called green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis. Alpha hemolysis is generally caused by peroxides produced by the bacteria.

Beta hemolysis (β-hemolysis) is caused by a complete lysis of the red cells in the media. The area around and under the colonies are lightened and transparent. Streptococcus pyogenes, or Group A beta-hemolytic Strep, displays beta hemolysis. Beta hemolysis is sometimes called complete hemolysis. Beta hemolysis is caused by hemolysins.

Some weakly beta hemolytic species will cause intense beta hemolysis when grown together with a strain of Staphylococcus. This is called the CAMP test¹. Streptococcus agalactiae displays this property.

If an organism does not cause hemolysis, it is said to display gamma hemolysis (γ-hemolysis): the agar under and around the colony is unchanged (this is also called non-hemolytic). Enterococcus faecalis (formerly called Group D Strep) displays gamma hemolysis.

Notes

¹The CAMP test is so called from the initials of those who initially described it, R. Christie, N. E. Atkins, and E. Munch-Peterson.

References

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.